Catalytic cracking of hydrocarbon oils



9 E947. J. M. BRACKENBURY 2,432,277

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Patented Dec. 9, 1947 `UNITED STATES PATENT oFFlcE 2,432,277 cA'rALY'rIcoutremer* maocARoN John M. Brackenbury, Oakland, Calif., assigner toShell Development Company, San Francisco, Calif., acci-poration ofDelaware.

Application January 2, 1945, Serial No. 571,101

This invention relates to the catalytic cracking of hydrocarbon cils toproduce valuable normally gaseous and normally liquidhydrocarbonproducts of lower molecular weight and boiling range than theoil feed. More particularly the invention relates to catalytic crackingwith finely divided crackingcatalysts in iiuidized or pseudo fluidcatalyst systems wherein the catalyst is continuously recycled throughthe conversion zone and through a separate regeneration zone. In themethod described the material is separated into a more refractoryfraction and a less refractory fraction and these fractions aresimultaneously treated in a single reaction Zone at diiferent spacevelocities. This is accomplished 3 Claims. (Cl. 196-52) by charging themore refractory fraction and the l fresh catalyst to the bottom of aiiuidized bed of the catalyst in the reaction zone and introducing theless refractory fraction at an intermediate point into the saidfluidized bed. In a specific embodiment the method is applied for thesimultaneous catalytic cracking of a refractory heavy vacuum flashedcondensate and a more refractory light naphtha fraction from partlyreduced crude petroleum. The process of the present invention makes useof the above described principles in the treatment of specific feedmaterials and involves, in'addition, certain additional findingsregarding the refractivity of certain feed stocks and the simultaneouscracking of mixtures of feed materials, which materials per seordinarily require differenttreating conditions for optimum results.

In the catalytic cracking of hydrocarbon oils with clay type crackingIcatalysts it is found that the following principles generally apply:

(i) 4Higher molecular "weight hydrocarbons of any given type are muchmore susceptible to cracking than lower molecular weight hydrocarbons.

(2) Oieiins, in general, are more susceptible to cracking thannaphthenes.

(3) Naphthenes are, in general, more susceptible to cracking thanparamns.

2 -(4) Parafiins are, in general, more susceptible to cracking thanaromatics.

(5) Aromatics are, in general, quite refractory. particularly thepolycyclic aromatic hydrocarbons such as naphthalene.A

When a hydrocarbon oil to be cracked, for instance a gas oil, iscontacted with the catalyst under suitable cracking conditions, thevarious m.-

terials which are more susceptible to cracking arey cracked and there isproduced 'a hydrocarbon mixture containing cracked products of thedesired boiling range, for instance gasoline as well aspartially crackedproducts of intermediate boiling range and some unconverted materiak Thematerial boiling above the desiredboiling range is generally highlyaromatic and is more refractory than the initial feed stock,particularly for catalytic cracking. If it is' desired to furtherconvert this refractory `material it is generally treated by thermalmethods, although in a few cases it has been suggested to treat itcatalytically under more drastic conditions than those prevailing in thefirst cracking step.' This latter suggestion is not, however, generallyused because the large investment and costs incurred` by a secondcatalytic cracking plant for this purpose is prohibitive. `and becauseblocked out operation in a single plant cuts down plant capacity, andbecause the yield and gasoline to carbon ratio are poor.

In the process of the invention this higher boiling more refractorymaterial, or a fraction of it, is recycled and catalytically cracked atessentially the same temperature. Recycle of the higher boiling'refractory material leads to particularly favorable results. In thefirst place, it is found that in spite of -the refractory nature of therecycled material, excellent yields of gasoline and other valuableproducts may be obtained from it without increasing the temperature ofthe cracking treatment. Furthermore, the presence of this refractorymaterial in the cracking zone with the original feed does not decreasethe Droduction of cracked products. In many cases the recycled stock maybe catalytically cracked without reducing the throughput capacity of theplant` with respect to `fresh feed. Furthermore, this operation does notresult in any decrease in the gasoline to carbon ratio. Furthermore,practically all of the cracked products from the cracking of therecycled stock boil within the gasoline boiling range. Furthermore, thegasoline produced by cracking the feed stock and the recycled stocksimultaneously is of particularly good quality and is superior to thegasoline produced bythe catadrawn to scale.

lytic cracking of the original feed alone under the same conditions. Forexample, when cracking a flashed condensate from a West Texas reducedcrude with the commercial synthetic silicaalumina cracking catalyst in afluid catalyst system under the following conditions:

Temperature 950 F. Pressure Substantially atmospheric Weight hourlyspace velocity 1. Catalyst/oil .ratio 12:1

' the following products and results were obtained:

Per cent by weight Conversion c 65 Debutanized gasoline (325 F.) 20. 0Normally gaseous hydrocarbons 29. '7 Higher boiling products (325 F.+)42. 2 Coke ...l 8. 1

Various fractions of the 325 F.+ material were separated and recycled indifferent amounts. When all of the S25-475 F,fraction was recycled.(without changing the first feed rate) the following results wereobtained:

. Per cent by weight Conversion L 67 Debutanized gasoline (325 F.) 29.3Normally gaseous hydrocarbons 29.1 Coke 8.6

When 50% of the 600 F.{ material was recycled the following results wereobtained:

Per cent by weight Conversion reas 67 Debutanized gasoline (325 F.) 27.9Normally gaseous hydrocarbons 26.4 Coke 8.1

According to the process of the invention, the

higher boiling more refractory material, Aor a with the attached drawingwherein the more lmportant apparatus and flows of one typical operationare illustrated by conventional figures not' Referring to the drawingthe hydrocarbon oil to be cracked, for instance a heavy gas oil, areduced crude or the like, is, fed by pipe I and pump 2 through heatingcoil 3 in a suitable furnace 4. The heated oil passes to a tar separator5 from which unvaporizable heavy liquid materials may be withdrawn vialine 6. The hydrocarbon vapors passed via line l to the middle portionof a fluid catalyst reactor 8 filled with a continuously renewed bed offluidized finely divided cracking catalyst. The incoming vapors aredistributed throughout the middle of the catalystV bed by means of aballled distributor plate 9 or other equivalent means. This arrangementdiffers from previous cracking processes withdrawn via line 20.

to a fractionating column I3 wherein they are separated into a fractioncontaining normally gaseous products and cracked gasoline of any desiredend point and a heavy fraction. The lighter `fraction is taken overheadvia line I4 to a condenser I5 and separator I6. Part of the condensatemay be recycled via line Il and Dump I8, and the remainder may bewithdrawn via line I9 and treated in any conventional manner.

The heavier fraction from column I3 may be removed as a single bottomproduct or it may be removed as two separate fractions. In such caseswhere it is desired to fractionate the material into more closely cutfractions, it is desirable to remove the bottom product as two separatefractions. Thus, a fraction of heavy oil containing a small amount ofsuspended catalyst (which escaped separation in the separator I0) may beThis may be discarded but is preferably cycled via lines 2| and 22 backto the reactor. A clean fraction of the heavy oil may be removed vialine' 23 and passed to a separate stripper or fractionator 24. Infractlonator 24 any desired portion 0r fraction of the heavy oil, say aS25-475 F. cut may be separated and removed overhead via'line 25. Theremainder may be withdrawn via line 26 as a product of the process. g

The heavy oil in line 25 consists largely of refractory uncracked and/orpartially cracked products from the primary cracking step described,This oil picks up hot freshly regenerated catalyst from the regeneratedcatalyst standpipe 21 and the mixture passes via line 22 to the reactor8. This mixture is introduced into the reactor at or near the bottom vlathe distributing baie arrangement 28. The oil vapors 'pass up throughthe fluid catalyst bed and after reaching baille 9 commingle with thefresh feed introduced as described above.

Partially spent catalyst is continuously withdrawn from the lower end ofthe reactor 8 via stripping section 29 and standpipe 30. Steam or othersuitable gaseous agent is added via line 3| and distributor 32 near thebottom of the stripping section to replace the oil vapors in thefluidized catalyst being withdrawn. The partially spent catalystwithdrawn via 30 is picked up by a stream of regeneration gas, forexample, air or a mixture of air and flue gas and carried via line 33 toa conventional regenerator 34. The spent regeneration gas andregenerated catalyst pass to a cyclone separator 35. The spentregeneration gas is withdrawn via line 36 and the regenerated catalystis withdrawn via standpipe 21.

The process of the invention is applicable for the catalytic cracking ofvarious hydrocarbon oils boiling above the gasoline boiling range. Thusit can be applied in the cracking of naphthas, kerosene distillates,stove'oils, and gas oils. These stocks may be catalytically cracked atthe usual temperatures in the order of 800 F. to 925 F.

The process is particularly advantageous for the catalytic cracking ofheavy stocks such as i boiling product fraction and a higher boilingrede-asphaltized reduced crudes, vacuum iiashed distillates such asdescribed in my above-mentioned copending application, and lother suchstocks having an average molecular weight of 280 or above. Such stocksusually Icontain considerable concentrations of nitrogen compounds,sulfur compounds, oxygen compounds, small amounts of asphalticsubstances, waxes etc. They do not, in general, produce the best,vquality gasoline in once-through catalytic cracking'oper- 10 ations andare more advantageously cracked at high temperatures of at least 950 F.to produce large quantities of valuable olens and a gasoline which canbe converted into a first quality product by a simple second treatmentsuch as a repassing treatment at a lower temperature or a selectivehydrogenation treatment.

I claimas my invention: l

1. In a process for the catalytic cracking of a\ hydrocarbon oil toproduce valuable normally gaseous and normally liquid hydrocarbonproducts of lower molecular weight and boiling point in a catalyticcracking system using a fiuidized nely divided cracking catalyst, themethod of operation comprising the steps of introducing the freshhydrocarbon oil feed to be cracked at one or more intermediate pointsinto a bed of continuously replenished uidized nely Ydivided crackingcatalyst constituting the cracking zone wherein it is catalyticallycracked in the presence of recycle stock introduced as hereinafterspecifled, continuously withdrawing spent catalyst from said uidized bedand continuously regenerating said withdrawn spent catalyst in aseparate regeneration zone by burning carbonaceous deposits therefrom,separating from the product from said cracking zone by fractionation alower cycle fraction consisting largely of uncracked and partiallycracked products of said feed,fcontact 40 ing at least a portion of saidhigher boiling fraction with the hot freshly regenerated catalyst fromsaid regeneration zone and passing the mixture to said cracking zone byintroducing said mixture at the bottom of said bed of iiuidized nelydivided cracking catalyst, thereby to simultaneously crack said-freshhydrocarbon feed and said recycled fraction in the same bed of'fiuidizedfinely divided cracking catalyst at different space velocities whileavoiding contact of the said fresh 59 hydrocarbon feed with said hot,freshly regenerated catalyst. ,V

. 2. In a process for the catalytic cracking of a hydrocarbon oil toproduce valuable normally gaseous and normally liquid hydrocarbonproducts of lower molecular weight and boiling point lin a catalyticcracking system using a uidized finely divided cracking catalyst, themethod of operation comprising the steps of introducing the freshhydrocarbon oil feed to be cracked at one 60 or more intermediate pointsinto a bed of continuously replenished nuidized finely divided crackingcatalyst constituting the cracking zone wherein it is catalyticallycracked in the presence of recycle stock introduced as hereinafterspecied continuously withdrawing spent catalyst from said iiuidized bedand continuously regenerating said withdrawn spenticatalyst in aseparatey regeneration `zone by burning carbonaceous deposits therefrom,separating from the product from said cracking zone by fractionation alower boiling product fraction and a fraction boilingV between about 325and 475 F. consisting largely of uncracked and partially crackedproducts of said feed, contacting at least a portion of said S25-475 F.fraction with the not freshly regenerated catalyst from saidregeneration zone"'and passing the mixture to said cracking zone byintroducing said mixture at the bottom of said bed of nuidized finelydivided cracking catalyst, thereby to simultaneously crack said freshhydrocarbon feed and said recycled fraction in the same bed of iiuidizednely divided cracking catalyst at different space velocities whileavoiding contact of the said fresh hydrocarbon feed with said hotfreshly regenerated-catalyst.

3. In a process for the catalytic cracking of a. hydrocarbon roil toproduce valuable normally gaseous and normally liquid hydrocarbonproducts of lower molecular weight and boiling point ina catalyticcracking system using a fiuidized finely divided cracking catalyst, themethod of operation comprising the steps of introducing a straight rungas oil having a molecular weight above about 280 at one or moreintermediate points into .a bed of continuously replenished uidizedfinely divided cracking catalyst constituting the cracking zone whereinit is catalytically, cracked in the presence of recycle stock introducedas hereinafter specified, continuously withdrawing spent catalyst fromsaid fluidized bed and continuously regenerating said spent catalyst ina separate regeneration zone by burning carbonaceous deposits therefrom,separating from the product from said cracking zone by fractionation alower boiling product fraction and a higher boiling fraction consistinglargely of uncracked and partially cracked products of said feed,contacting at least a portion of said higher boilingfraction with thehot freshly regenerated catalyst from said regeneration zone and passingthe mixture to the cracking zone by introducing said mixture at thebottom of said bed of fiuidized finely divided cracking catalyst,thereby to simultaneously crack said hydrocarbon -feed and said recycledfraction in the same bed of iiuidized nely divided cracking catalyst atdifferent space velocities while avoiding-contact of the freshhydrocarbon feed with said hot freshly regenerated Catalyst.

` JOHN M. BRACKENBURY.

REFERENCES CITED The following referencesV are of lrecord in the file ofthis patent:

` UNITED STATES PATENTS Alther Feb. 12, 1946

